In the forthcoming grant period the High Voltage Electron Microscope (HVEM) Facility at the University of Colorado in Boulder will continue to divide available operating time between applicants from outside the University and investigators within the Department of Molecular, Cellular and Developmental Biology. Greater emphasis will be placed on the taking of stereo pairs of micrographs the better to take advantage of the HVEM's capacity to provide images of thick biological preparations and thus reveal the fine structure of biological systems in three dimensions. The techniques required for taking and displaying stereo images are under continuing improvement toward the end of making them ever more valuable. Within this period it is planned as well to record stereo images in digital form from serial sections and to reconstruct in isolation a number of intracellular systems which otherwise are unavailable for viewing in their entirety. A recently completed cold stage will be activated in the hope of studying frozen-dried specimens and thus avoiding some of the artifacts that are a worrisome product of procedures employing chemical fixatives. Toward the same end, though not through changing fixation, samples of whole tissues will be embedded in water soluble matrices and thin-sectioned for viewing after the matrix has been removed and the section dried by the critical point method. Such preparations provide convincing evidence that a substantial part of the material in conventional epoxy sections is never seen because the resin has electron scattering properties equivalent to the material embedded. Finally a more intensive effort will be made to use immunocytochemical procedures to map the distribution of specific intracellular proteins used as antigens.